Metabolic and productive characterisation of multiparous cows grouped for fat-corrected milk yield and milk protein concentration

Objective of this study was to determine health and productivity of
cows grouped for fat corrected milk yield and protein
concentration. Therefore 23 cows (6 cows with high FCM and high
protein content, 5 with low FCM and low protein, 7 with high FCM
and low protein and 5 cows with low FCM and high protein
concentration) were examined from two weeks before parturition
throughout the first 22 weeks of lactation. Regularly, milk and
blood samples were collected and body condition observed. Cows were
subjected to 30% feed restriction in early (d 26 to 28 pp) and
mid-lactation (d 141 to 143 pp) to evaluate metabolic reaction.
Three intravenous glucose tolerance tests (ivGTT; d -14, 20 and 127
pp) were conducted to assess differences in insulin response.
Furthermore hepatic gene expression profiles were examined at day
of parturition, d 15, 57 and 155 pp as well as at the last day of
both feed restriction periods. Measured target genes (20) play key
roles in glucose transport, lipid, protein and carbohydrate
metabolism as well as in ketogenesis. Milk, blood serum and body
condition parameters revealed highest risk for metabolic imbalances
of high yielding dairy cows during early lactation. Gene expression
profiles indicated that high yielding and especially cows with high
FCM and low protein concentration had higher risk for fatty liver
development and diminished gluconeogenesis potential. Also, during
feed restriction in early lactation, these cows seemed to have
reduced physiological adaptation capacities to the exacerbated
energetic imbalance. Nevertheless, results of ivGTTs suggest that
high yielding cows show gluconeogenesis activity meeting demands of
milk synthesis in early lactation and cows with high FCM and
protein concentration even seemed to exceed the needs of mammary
gland. Insulin sensitivity was reduced in high yielding dairy cows
prior to parturition. Furthermore only cows with low FCM and high
protein content were able to restore body reserves in
mid-lactation. Regarding results of hepatic mRNA abundance and
ivGTTs, those cows seemed to be in an improved energetic situation
compared to other cows. Moreover, high protein cows showed highest
insulin resistance in early lactation. Property of cows with low
FCM and low protein concentration was a difference in metabolism
due to seemingly enhanced protein catabolism instead of lipolysis.
Additionally, protein composition of milk was analysed throughout
experimental period with capillary electrophoresis on a chip
(Agilent Protein 80 Chip for Bioanalyzer). Cows grouped for FCM
yield and protein concentration showed differences in
concentrations of major milk proteins α-lactalbumin,
β-lactoglobulin, α-, β- and κ-casein, which could be explained by
their different genotypes of β-LG and κ-CN: high yielding cows
showed lower casein concentrations compared to low yielding cows.
Furthermore, low yielding cows had lower contents of α-CN.
Composition of milk protein was almost not altered by restricted
feeding. Solely restricted feeding in mid-lactation resulted in
decreased mean contents of κ-CN and therefore potentially
diminished processing quality of milk for cheese making.